If you are responding to a job posting on LinkedIn or perhaps another online venue, you may be given the option of submitting a cover letter.
The problem lies in where that actual cover letter ends up. The key to a successful cover letter is that it needs to be addressed to the person who is in the best position to act upon it.
In a large, corporate environment, your cover letter may just go right into the trash, without anybody ever reading it. In smaller working locations it may be possible to learn the name of the hiring manager or perhaps the personnel manager.
Conversely, there is an advantage to creating a cover letter even if you don’t actually send it to anybody. It can help clarify in your mind what job you are applying for, why you think you’re worthy of being interviewed and what you bring to the table.